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Effect of Prostaglandin F_2α on Growth of Mycoplasma bovis Associated with Bovine Mastitis

Ahmadzadeh A, Fox LK, McGuire MA, and Carnahan KG

Mycoplasma bovis (M. bovis) is a major mastitis pathogen that has been reported to be refractory to antibiotic treatment. Certain fatty acids have been shown to inhibit the growth of mastitis pathogens such as Staphylococcus aureus (S. aureus). In vitro experiments were conducted to determine the effects of prostaglandin F2α (PGF2α) on growth of M. bovis. Five strains of M. bovis of bovine origin were selected for the study. Two strains were reference strains (ATCC 25025 and 25523) and the other strains were isolated from diseased cattle. Isolates were cultured and suspended in saline to achieve an optical density of 0.2 at 520 nm, a suspension of approximately 1 × 107 to 2 × 108 CFU/ml. Subsequently, M. bovis suspensions were incubated in culture media containing PGF2α (dinoprost tromethamine) at final concentrations of 0 [control), 2, 4, and 8 mg/ml, for 8 h at 37°C. A sample from each treatment group was obtained and cultured on agar plates for 10 d and bacterial growth assessed as CFU/ml. The entire experiment was repeated four times using duplicate tubes per PGF2α concentrations for each strain. Data were analyzed by ANOVA and the model included the effect of treatment, strain, and their interaction. Treatment affected (P<0.01) M. bovis growth, and mean CFU/ml decreased with concentrations of PGF2α at 4 and 8 mg/ml but not 2 mg/ml (43.6, 42.1, 24.3, 7.8 [±1.1] for 0, 2, 4, 8 mg/ml, respectively). However, an effect of treatment by strain interaction on mean CFU/ml was detected (P<0.05), indicating that the effect of PGF2α on bacterial growth was not consistent across strains. Overall, the 2 mg/ml PGF2α decreased CFU/ml in only one strain compared with control, whereas 4 and 8 mg/ml PGF2α decreased CFU/ml in all strains compared with control. These in vitro results provide evidence, for the first time, that the fatty acid PGF2α, in the form of dinoprost tromethamine, has inhibitory effects on growth of M. bovis, and this bacteriostatic effect appears to be strain and dose dependent.